The present invention relates to an apparatus for relative adjustment of axially-spaced lens components of an optical system and more particularly to such an apparatus wherein selectively changing the speed and amount of magnification and adjusting the focus can be effected by a single control member.
In the prior art, it is well-known that an objective lens component for focusing and a zoom lens component for zooming, and a compensating lens component, are spaced apart and are movable axially, relative to a basic lens component mounted on a fixed frame in the optical system. It is also well-known, as for example, shown in U.S. Pat. No. 3,765,748 to Mito that both focusing and zooming can be effected with a single control member. In the structure disclosed by Mito displacement of an operating member in the axial direction thereof controls zooming while rotation of the same member about its axis effects focusing. However, in Mito the mechanism for zooming and focusing is mechanically coupled to the operating member so that the amount of magnification is directly proportional to the axial displacement of the operating member and the amount of movement of the focusing component is directly proportional to the amount of the rotation of the operating member.
Similarly, in the patent to Back U.S. Pat. No. 3,455,628 a movable ring is mounted for both longitudinal movement and rotational movement. The movable ring is directly mechanically coupled to the zoom component and to the focusing component for moving either or both of the latter depending upon the movement imparted to the operating member. The amount of displacement of both the focusing or zooming component in the latter prior art construction is directly proportional to the amount of displacement longitudinally or rotationally, as the case may be, of the movable ring.
While it is also known, for expensive and large lens systems, such as, for example, those used with television cameras, to drive the zoom component with an electric motor drive, these drives are usually not speed adjustable and in those instances where a variable speed drive is provided the operator is required, in advance, to choose one of a plurality of speed settings prior to zooming and thereafter to control zooming with an on-off switch.
In another prior art device, namely U.S. Pat. No. 3,241,470 to Brolde, there has been disclosed a drive system for lenses in which an electric drive motor is connected in series with an adjustable resistor. The circuitry disclosed is stated to be such as to maintain a constant driving speed at any speed which is preselected.
Not only, therefore must the operator when using one of these prior art devices use one hand for operating the zoom control switch (after having preset a selected speed for the zooming) but requires his other hand for the focusing adjustment. It should be noted here that while zoom systems almost invariably contain focus compensating lenses for roughly adjusting the focus by "tracking" the zoom lens movement, nevertheless, manual fine focusing is invariably required. Manual focusing is also required for focusing on objects at different distances.
In the case of two separate operating members for focusing and zooming, third functions, for example, color adjustments (for color television), video level adjustments, iris control adjustments and others become extremely difficult since both the operator's hands are already required for manipulating the separate zoom and focus controls.